The desire to reduce the draft of propeller driven marine craft has long existed, and a variety of proposals has been made for reducing the hull draft while accommodating a propeller, examples being shown in U.S. Pat. Nos. 872,389; 1,007,583; 1,059,806; 3,469,549 and 3,744,446. Various concepts are used with such propeller pockets such as tunnels, channeling devices, and varying cross section configurations. While a number of the proposed designs do offer advantages of one aspect or another, many shallow draft tunnels and channels are unacceptable for high speed watercraft in that cavitation problems at the propeller are aggravated, steering is adversely affected, and installation of the propeller shaft and driving gear is difficult.
It is an object of the invention to provide a propeller pocket for relatively high speed watercraft which may be used with either inboard, inboard/outboard, or outboard propeller drives, and wherein propeller cavitation is minimized.
Another object of the invention is to provide a shallow draft pocket for propeller driven watercraft wherein the configuration of the pocket may be incorporated into a wide variety of hull forms, and the installation of inboard driving gear is simplified.
A further object of the invention is to provide a shallow draft pocket for propeller driven marine craft wherein the pocket configuration aids in supplying the propeller with water with a minimum of turbulance wherein cavitation at the propeller is substantially eliminated within normal operating speed ranges.
In the practice of the invention the shallow draft pocket is defined by a plurality of planar surfaces formed in the watercraft hull adjacent the stern. A planar transition surface obliquely oriented upwardly and rearwardly intersects an upward obliquely defined surface which extends toward the hull's stern. The lateral sides of the upper surface are intersected by obliquely disposed side surfaces upwardly converging and intersecting the upper surface to form a uniformly decreasing upper surface width in the direction of the stern. The upper surface engages a deflection surface intersecting the stern which is, preferably, slightly obliquely oriented to the horizontal in a downward direction, and the resultant water flow of these surfaces provides an adequate supply of water, at low turbulence, to the propeller region.
In an inboard powered installation, a propeller shaft recess intersects the pocket upper surface and includes a surface substantially perpendicularly disposed to the propeller axis, and the presence of this recess, plus the presence of a positioning depression located adjacent the upper surface, greatly aids in simplifying the installation of an inboard propeller drive within the pocket of the invention.